PROJECTSUMMARY Foodallergy(FA)isapotentiallyfataldisorderinneedofimprovedmethodsfordiagnosis,clinicalmonitoring, andtreatment.Basophils,theleastcommonofthebloodgranulocytes,havebeenimplicatedasimportant contributorstothepathologyofFAandfood-inducedanaphylaxis.Certaincellsurfacephenotypicfeaturescan helptoidentifybasophilswhichhavebeenactivatedbyallergicmechanismsinvivoorinvitro.Inthisproject, wewilldeterminewhetherphenotypicandfunctionalfeaturesofbloodbasophilscanbeusedaspartofan approachtopredicttheseverityofclinicalreactivitytofoodallergensinpeoplewithFAinducedbymultiple foods(herein:multi-FA),toimprovethesafetyandefficacyoforalimmunotherapy(OIT)protocolstotreatFA, and,inprinciple,tocustomizeimmunotherapyprotocolsforeachindividualfoodallergicperson. InAim1,wewillperformdetailedimmunophenotypingtomonitorthephenotype(s)andactivationstatusof basophilsandtheirsubpopulationsinthebloodofparticipantswithmulti-FA,asmeasuredexvivoatbaseline (definedhereinaswithoutexvivostimulationwithallergensoranti-IgE).Bloodwillbeobtainedbeforethe patients?enrollmentinapilot,mechanistic-focused,phase2clinicaltrialofmulti-OIT(definedassimultaneous OITwithmultiplefoodallergens)conductedwithorwithoutomalizumabordupilumabandatmultipleintervals duringthecourseofandaftertheendofsuchimmunotherapy(IT)(seeProject1);?wealsowillanalyzeblood frommulti-FAparticipantsnottreatedwithOIT,atopicpeoplewithoutFA,andhealthynon-atopiccontrols.This workwilltestthehypotheses:1)thattheexpressionofactivationand/orothermarkersinbloodbasophilsof multi-FApatientsatbaseline,beforethecells?exvivostimulation,correlateswiththepatients?acuteclinical reactivitytofoodallergensbeforeandduringITandcanbeusedtomonitorthedevelopmentanddurabilityof desensitizationand/orsustainedunresponsiveness/?tolerance?inducedbyIT. InAim2,wewillperforminvitrostudiesofbasophilphenotypeandfunction(i.e.,basophilactivationtests [BATs]),tomeasurebasophilresponsestochallengewithfoodallergensexvivo.Thisworkwilltestthe hypothesisthat,inmulti-FApatients,themagnitudeofchangesinbasophilphenotype(e.g.,expressionof activationmarkers)and/orfunction(e.g.,secretionofmediators)inducedbychallengeoftheirbasophilswith foodallergensexvivocorrelateswiththereductioninclinicalevidenceoffoodallergensensitivityduringITand mayalsocorrelatewithclinicaloutcomesofdesensitizationvs.sustainedunresponsiveness/?tolerance?. Oneofourkeylongtermgoalsistodevelopinnovative,rapid,andreliablemethodstomonitorbasophil phenotypeandfunctionthatcanbeusedclinicallyforsuchpurposesaspredictingaperson?sclinicalsensitivity tofoodallergens,predictingtheclinicaloutcomeofOIT,customizingOITandotherITprotocolsforindividual people,and/ormonitoringthedevelopment,effectiveness,ordurabilityofimmunotherapy.